It is known in the art that some chemical compounds reversibly change color when in contact with water. An example of such a chemical compound is cobalt chloride which is blue in its anhydrous state (i.e., CoCl2) and pink in its full hydrated state (i.e., CoCl2.6H2O).
U.S. Pat. No. 3,951,098 (Meyers) relates to a moisture indicator useful for the monitoring of the moisture content of a potting soil of a conventional house plant. More particularly, this indicator includes a plastic housing encapsulating an elongated wick extending from a lower point where it is exposed beneath the soil level to an upper point in an indicator chamber formed in the housing. The wick surrounds but does not touch a “signal element” comprising a layer of moisture-sensitive, color changeable substance (e.g., cobalt chloride), to carry moisture to the vicinity of the “signal element”. The substance changes color in response to predetermined gains (or losses) in moisture content.
U.S. Pat. No. 4,184,445 (Burrows) relates to a moisture indicator for use in determining the wet-dry cycle of soil surrounding cultivated plants. It comprises an upper chamber and lower chamber with an interconnecting passageway across which an absorbent supporting material (e.g., blotting paper) impregnated with a moisture sensitive indicator composition (e.g., cobalt chloride) is positioned. The lower chamber has a bottom opening which upon insertion into the soil results in the relative humidity in the lower chamber being related to the wetness of the soil. The upper chamber is partially transparent and may optionally be vented to the outer atmosphere.
Existing cobalt salts are susceptible to being washed out into the surrounding substrate, thereby involving only a short useful life of a moisture indicator containing the same, and also involving contamination of the soil. In this regard it is to be noted that companies using cobalt chloride have released Material Safety Data Sheets (MSDS) describing cobalt chloride as a skin and respiratory irritant. Also, MSDS reports on the carcinogenic properties of cobalt chloride vary; some state that there is no risk while others say that cobalt chloride has caused cancer in laboratory animals. The warning label that comes with cobalt chloride is that any exposure can irritate the lungs and skin and that long term exposure can affect the heart, kidneys, lungs, and thyroid. Protective eyewear, gloves, respirators and ventilation hoods are the recommended protection measures for handling cobalt chloride. Furthermore, companies using cobalt chloride as the indicator in their indicating Silica Gel are putting their employees and consumers, as well as the environment, at unnecessary risk. British regulations have required that cobalt chloride be handled and disposed of as a hazardous material since 2001. Cobalt chloride, if not properly disposed of, can leach into the ground and water supply, contaminating both.
A non-cobalt chloride, appearance-changing moisture indicator is described in U.S. Pat. No. 6,058,647 (Emalfarb). The indicator has a body made up of a porous material that changes in physical appearance with a change in the amount of moisture retained in the porous material. In the operative state, a first part of the sensor body resides within the growing medium and a second part of the sensor body remains visible to allow a user to ascertain through the appearance of the second part of the sensor the amount of moisture in the growing medium. The moisture content is ascertained by “darkening” of the porous material in the state with more moisture. The shortcoming of this indicator is that differentiating between shades of the same color can be difficult.
As illustrated by the above mentioned prior art documents, color/appearance changing moisture sensitive indicators either require the assembly of multiple parts for supporting a porous absorbing material that is impregnated with a hazardous moisture sensitive indicator substance such cobalt chloride or they incorporate using a porous material that only changes appearance by different levels of darkening of the same color that is difficult to differentiate visually.
Therefore there is a strong need for a substrate moisture indicator that is inexpensive to manufacture, durable, does not require assembly of multiple parts and clearly reveals the dryness/wetness of the substrate. Also, there is a strong need for a substrate moisture indicator that naturally blends with the surrounding environment. Furthermore, there is a strong need for a moisture indicator that has an extended useful life, prevents contamination of the soil and avoids any negative effects on the health of persons using the indicator. The present patent application puts forth a moisture indicator that meets these aforesaid needs.